Received from the
Department of Anesthesia, University of Toronto, Toronto General
Hospital, Toronto, Ontario, Canada.

Statements

The author was consultant to Saturn
Biomedical Systems (Burnaby, British Columbia, Canada) and is currently
consultant to Verathon
Medical (Bothell, Washington, United States), the manufacturers of the
GlideScope

Interestingly, the father of laryngology, Manuel Garcia, was neither an
anesthesiologist nor a laryngologist (3). He was an opera instructor intrigued by the
larynx, a seemingly simple organ capable of producing a rich
range of sounds. Not only are these short bands of tissue
occasionally able to produce extraordinarily beautiful music,
they are the principal means by which we communicate. Many
people including teachers, religious leaders, entertainers, and
alas politicians and lawyers depend upon the larynx for their
livelihood. Even minor laryngeal injuries to them can result in
significant disability. The vocal cords are even more densely
innervated than the muscles responsible for facial expression
(25). Moods and attitudes are conveyed through extraordinarily subtle
alterations in voice as evidenced by our ability to communicate
with infants and domesticated animals even when our words have
no meaning.

The larynx is a deceptively complex instrument that
we can better understand using stroboscopic instruments that
allow synchronization of light and vocal fold frequencies.
Slight variations in vocal fold tension produce sound when
tracheal air, under pressure, is presented to them. To produce
quality and variable sound, their mucosal surfaces, particularly
their edges, should be smooth, pliable, elastic, capable of
close apposition, and very precise adjustments of tension. These
folds produce the sound; the pharynx, oral cavity, and nose serve
as a resonating chamber. As laryngoscopists, it is important for
us to make every effort to perform our tasks with the greatest
of respect for so sensitive and vital a structure.

Yet consider how we achieve our airway objectives? We open the
mouth widely, extend the neck, insert cold steel between the
teeth, and apply upward force (distracting and compressing the
tongue, elevating the mandible, applying tension to the delicate
tonsillar pillars, engaging the vallecula or epiglottis, and
hoisting it skyward) in an effort to visualize a structure that
is concealed for its own protection. Each one of these maneuvers
is capable of resulting in injury and each may fail to achieve
its objective. If we are only partially successful, we may
introduce a tracheal tube (TT) without having completely
visualized the target.

Prior to the introduction of the standard laryngeal mask airway
(the LMA Classic;
Laryngeal Mask Company, Henley on Thames, United Kingdom), airway management
(AM) had
not
changed very much since Janeway performed tracheal cannulation
in 1913. We have continued to use the same crude line-of-sight
laryngoscopes Miller and Macintosh communicated in 1941 and
1943, respectively. These devices are inexpensive, pervasive, and
difficult to learn; to some extent, this expertise helps to define
our specialty. Yet we know that even in the best of hands, there
are patients with anatomical characteristics that do not favor
successful visualization of laryngeal structures. Furthermore, we know that
there is an irreducible number of patients, perhaps 8.5 percent
(21), in whom direct laryngoscopy (DL) unexpectedly fails. So far, our attempts at
finding an intubating position that achieves alignment of the "anatomical axes” has yielded the flexion/extension (sniffing),
neutral, simple extension, and flexion/flexion positions (13,
16). It
would appear that we have exhausted the combinations but have yet
to find a position that achieves the objective.

To date, our focus has been on catastrophes and serious injuries
associated with tracheal intubation (1,
8, 10). These include failed or delayed tracheal intubations that may result in
esophageal injuries, mediastinitis, persistent or profound
hypoxia, aspiration, brain injury, and death. We have also looked
at cervical, dental, laryngeal, and tracheal injuries.
Furthermore, we know that multiple attempts at DL and tracheal intubation are associated with hypoxemia, hypercapnia,
hypertension, unanticipated admission to the intensive care unit, and injuries to the
teeth, trachea, and esophagus (9). They may also be associated with
cardiac arrest and death (20).

There is an increasing number of
alternatives to tracheal intubation (represented by a vast array of supraglottic/extraglottic
airway devices). Likewise, there are numerous ways of tracheal
intubation not
requiring DL. Some of these are blind techniques [for example,
the digital, blind nasal, or lightwand-assisted technique and
blind tracheal intubation through the intubating laryngeal mask airway
(the
LMA Fastrach; Laryngeal Mask Company) and some of these are visual [for example, flexible
bronchoscopy-assisted (FBA) tracheal intubation using a LMA as conduit].
Up to now, our gold standard for managing the anticipated
difficult airway (DA) has been FBA tracheal intubation, and in skilled
hands, this remains the best, and occasionally the only likely
successful approach. Flexible fiberoptic bronchoscopes (FFBs) were designed for
versatility, not specifically for tracheal intubation. They can be used
to place bronchial tubes and blockers, to look through
tracheostomies, and to perform diagnostic/therapeutic procedures like bronchoalveolar
lavage and biopsies. Their complexity also makes them expensive,
complex, and fragile.

But lets look at another aspect of
FBA tracheal intubation. Assuming that we are able to direct the FFB into the
trachea, it is not uncommon to encounter difficulty advancing
the TT over the FFB. In fact, in the awake,
spontaneously breathing patient, this is often the most
challenging and for the patient, the most irritating part of
tracheal intubation. Johnson and co-workers (17) demonstrated that in 48 awake adults
with either known DAs or cervical spine injuries,
the TT impinged upon the right arytenoid (in 42
percent) or the
interarytenoid soft tissues (in 11 percent), often requiring multiple
attempts with TT rotation. Others have reported an even higher
incidence (40 to 90 percent) of such difficulties (17). FBA tracheal
intubation involves
visually-directed placement of the FFB; thereafter, the FFB functions much like a
flexible introducer. Maktabi and
co-workers (12) described 3 patients who underwent FBA
tracheal intubation and suffered injuries including vocal cord bruising, extensive
supraglottic swelling, and a very large pharyngeal hematoma. Clearly, such injuries are better than hypoxia, brain injury, or
death, but perhaps such injuries can be reduced if we can
achieve visualization of the laryngeal aperture, even in those challenging
patients, observing TT placement and advancement. Perhaps,
newer purpose-specific fiberoptic stylets and laryngoscopes or
video laryngoscopes will enable us to accomplish this.

The recent analysis of the American Society of Anesthesiologits Closed
Claims Project database found that only 17 of 87
tracheal intubation-associated laryngeal injuries were associated with
“difficult intubations” (10). Other studies led to the conclusion
that most laryngeal injuries are unrelated to the duration of
tracheal intubation. Either we do not know what “difficult intubation”
means or tracheal intubation, as conventionally performed is
problematic (18). Studying 80 adults with normal airways, Mencke
and co-workers (19) randomized them to tracheal intubation with or without a
neuromuscular blocker. They found that neuromuscular
blockade was associated
with better intubating conditions, a lower incidence of sore
throat, and fewer “vocal cord sequelae” (hematoma, mucosal
thickening, and granuloma, as determined by
video laryngostroboscopy). Such complications were more common
among patients in whom intubating conditions were less favorable.
Postoperative hoarseness can be quite persistent but rarely
comes to our attention. When either severe or persistent, it can
be quite disruptive to our patients.

Laryngeal edema may be a consequence of placing a round TT
through a triangular opening. This is consistent with the
observation of Tanaka and co-workers (23) who measured laryngeal resistance
before and after anesthesia administered via either a TT or a
standard LMA, and also performed endoscopic comparisons of the vocal cords of
the two groups. They found higher laryngeal resistance and
evidence of vocal cord swelling in the patients who had been
tracheally
intubated, though none of these tracheal intubations had been
difficult.

If we regard postoperative hoarseness or “vocal cord sequelae”
as complications of airway management, it provides incentive for
us to refine our techniques. Is it not incumbent upon us to
identify the causes of such injuries and to strive to reduce or
eliminate these complications? Should the lack of postoperative
hoarseness become a new quality indicator?

As discussed above, FBA tracheal
intubation essentially involves the blind
manipulation and advancement of the TT over a flexible
introducer. We are usually rewarded by our success and expect the patient to
be grateful for our talents despite the discomfort they may
experience. While laryngeal injury has been reported, it appears
to be rare; but could this be because we have not looked for it?
It seems logical that visualized placement and advancement of
the TT is likely to result in less laryngeal injury.
DL has been our standard method of achieving this. Unfortunately, we
must acknowledge that even in the best of hands, DL fails to
reveal the laryngeal aperture in a significant number of cases. Furthermore,
we are not particularly good at predicting the patients in whom
DL is likely to fail. It is time to correct our terminology; laryngoscopy
that does not reveal the laryngeal aperture is not difficult laryngoscopy, it
is failed laryngoscopy (4). Our airway assessment tools have been
calibrated specifically for DL; as faulty though they are for
DL, they likely have limited relevance to techniques other than
DL.

In their classic paper, Cormack and Lehane (7) recommended the use
of the “Oxford introducer” in situations when the epiglottis, but
not the laryngeal aperture could be seen. This device is now generally
known as the "gum elastic bougie" (GEB;
Smiths Medical, Watford, United Kingdom). In fact, they estimated that such a view occurs in 1
of 2000 obstetrical airways, a figure that seems to be much lower than
in
other studies. Combes and co-workers (2) prospectively evaluated a
strategy that employed the GEB after two unsuccessful attempts
at tracheal intubation by DL. One hundred out of 11,257 (0.9
percent) adult patients, unexpectedly could not be intubated and a
GEB
was used in 89 patients. This was successful in 90 percent (80/89
patients) but required two or
more (blind) attempts in half of these cases. Undoubtedly, this
low-tech approach is partly responsible for the popularity of
this technique, but we have to question whether a blind 90-percent solution (“successful” on the first attempt in only 41
percent of the patients) is an admirable strategy?

Rigid fiberoptic laryngoscopes [for example, the Bullard laryngoscope
(Gyros ACMI, Reading, United Kingdom), the UpsherScope Ultra
laryngoscope (Mercury Medical, Clearwater, Florida, United
States), or the WuScope System (Achi Corporation, San Jose,
California, United States)] have been on
the market for about two decades. They have their champions,
able to demonstrate the utility of these devices in the
management of many patients with DAs (5, 15). None is
dependent upon a line-of-sight and all provide high quality
laryngeal exposure with very limited tissue distraction or
compression. Each device is compatible with standard video
equipment enabling the display and/or recording of the
laryngoscopy and tracheal intubation process. Furthermore, each device positions
the eye of the operator, centimeters proximal to the larynx offering
a view of TT placement and advancement through the
laryngeal aperture.
They were developed specifically for laryngoscopy and tracheal intubation
and lack the versatility of the FFB. The
fiberoptic channels are protected within a rigid scope and are
therefore resistant to damage. Compared with FFBs, the acquisition and maintenance costs are low.
Why then, do they enjoy such limited popularity (22, 24)? Despite
their utility, they have significant learning curves - though
probably less than that required for either with conventional
laryngoscopes or FFBs - but lack a
sufficient cadre of committed enthusiasts. Unfortunately, even
the manufacturers and distributors lack the commitment to
support these products.

Several promising devices have recently become available, including though not limited to the
TrueView EVO2 laryngoscope (Truphatek, Netanya, Israel), the DCI
Video Intubation System
(Karl Storz Endoscopy, Tuttlingen, Germany), the GlideScope Video Laryngoscope (GVL;
Verathon Medical, Bothell, Washington, United
States), the McGrath Portable Video Laryngoscope (MVL;
Aircraft Medical,
Edinburgh, United Kingdom), and the Airtraq
Optical Laryngoscope (AOL; Prodol Meditec, Vizcaya, Spain) (5). These devices make use of telescopes, charge coupled device (CCD) technology,
or prisms to look around the anatomical corners: the TruView EVO2
laryngoscope employs an inexpensive
telescope angled at approximately 45 degrees; the DCI Video
Intubation System
uses a fiberoptic bundle coupled to an internal video camera,
directed approximately 25 degrees from the line-of-sight; the GVL consists of embedded
light emitting diodes (LEDs) to provide a light
source and a non-fogging CCD aligned at 60 degrees from the
line-of-sight; the MVL has a sliding disposable blade (one size fits for
all) and a small liquid crystal display screen attached to the handle;
and the AOL is a prism-based disposable device with a LED light source,
a non-fogging optical system, and a tube-guide channel for the TT.

These devices are all
relatively easy to use. Some have been more thoroughly
investigated than others, with manikins and normal and challenging
airways. A comprehensive review of these devices is beyond the
scope of this presentation. At the risk of seeming biased - and
bearing in mind, the disclosure of the author of this special
comment - the GVL has been the
most thoroughly tested. An early multi-centered study among
largely anesthesiologists with limited experience with the GVL yielded
99 percent Cormack-Lehane 1 or 2 views and a 96.4 percent
success of tracheal intubation (6). More recent studies involving anesthesiologists with formal GVL
training, yielded laryngeal views that were always equal to or
better than obtained by DL. An example of this is a recent
study reported from Vienna: Krasser and co-workers (14) performed both DL and GVL on 442 patients;
all tracheal intubations were successful (after a maximum of two
attempts), in 437 patients on the first attempt. The study
had a bias for enrolling patients with challenging airways; laryngeal exposure was achieved using
the GVL in every patient
despite not being able to accomplish this in 24 percent (105/442 patients)
using DL.

Another exciting approach involves the co-application of more
than one device to achieve tracheal intubation. The recently introduced
LMA C-Trach (Laryngeal Mask Company) and the LMA Fastrach in combination
with a lightwand (12) or a FFB are examples of this. Doyle (11) has described the
GVL to facilitate instruction of FBA tracheal intubation since it
enables the mentor to see precisely where the FFB is
placed (11). Used thusly, the GVL also provides tongue retraction,
directs the placement of the FFB and most importantly, enables
the operator to observe the insertion and advancement of the TT
through the laryngeal aperture. Levitan (emergency medicine
physician, Philadelphia, Pennsylvania, United States) has recently modified the Shikani Optical Stylet (Clarus
Medical, Minneapolis, Minnesota, United States), and proposes
that the Levitan FPS Scope (Clarus Medical) be used in conjunction with a conventional
laryngoscope, GVL, MVL, or
other such devices. Laryngoscopy is performed using a
laryngoscope and a TT, loaded onto the scope stylet, is
introduced under the epiglottis. The operator then diverts his
attention from the laryngoscope to the eyepiece of the scope
stylet,
observing the insertion and advancement of the TT.

DL is a legacy technique; it was introduced at a time when there
were no alternatives. We now have a wealth of supraglottic
airway devices and are able to safely avoid tracheal intubation in a
significant number of patients. But when tracheal intubation is deemed
appropriate, fiberoptic and video technology can generally
provide a laryngeal view, even in patients in whom this was
previously presumed to be difficult or impossible. Our current
airway assessment is predicated on DL. An anticipated difficult
DL does not mean that laryngoscopy will be difficult if DL is
not employed.

To summarize the advantages of these new techniques over DL:

The high upfront cost may be offset by predictable operating
costs. Compared with FFBs, they are robust and more resistant to
damage.

Fiberoptic and video laryngoscopes produce a higher proportion of
successful laryngeal visualizations than DL. Laryngoscopy that fails to
reveal the laryngeal aperture is failed laryngoscopy.

Tracheal intubation that succeeds despite failed visualization is a near
miss.

When DL fails, we try harder. More forceful elevation and
multiple attempts are associated with greater morbidity and
mortality.

Many of the newer techniques are easy to learn and can be easily
introduced into our practice. This is more applicable to
video laryngoscopy than rigid fiberoptic laryngoscopy.